At just 7.5p a serving, a toast sandwich is the cheapest lunch option, says the Royal Society of Chemistry. What other ultra-economical meals - of a similar order of simplicity - could be revived in these cost-conscious times?

As recipes go, it's even simpler than boiling an egg and as cheap as chips (even cheaper, in fact).

For a toast sandwich, take a very thin slice of bread and toast it. Once cold place it between two slices of bread, also sliced very thinly. Butter optional. Salt and pepper to taste.

Promoted by Victorian domestic goddess Isabella Beeton, this recipe comes from her 150-year-old Book of Household Management. Now the Royal Society of Chemistry wants to revive the dish to help the country through hard times.

But what's the appeal, beyond saving pennies? She recommended it as "very tempting to the appetite of an invalid", whose weak digestion was thought to benefit from plain food. Some who have tried it enjoy the textural variety between the cold crisp filling and the soft outer layers.

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Wartime treats - carrots on sticks

Food historian Annie Gray says Victorian-era recipes aimed at invalids fit the bill of cheap and quick to prepare. As well as the toast sandwich, beef tea was another favourite.

"That's as simple to prepare as simply boiling up beef bones to make a stock."

The toast sandwich isn't the only recipe in Mrs Beeton's compendium to use cold toast as the basis for a meal. She recommended toast soup - 1lb (0.45kg) of bread crusts boiled in 2oz (0.05kg) of butter and a quart (1.1 litres) of "common stock". Or for a refreshing drink, what about "toast-and-water"? Made with, you guessed it, a slice of stale loaf toasted, then soaked in a quart (1.1 litres) of boiling water until cold.

"If drunk in a tepid or lukewarm state, it is an exceedingly disagreeable beverage," warned Mrs Beeton. Quite.

Fitless cock

Another Victorian cookery writer was Charles Elme Francatelli, a former royal chef, who wrote A Plain Cookery Book for the Working Classes in 1852.

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How Mrs Beeton envisaged supper

"His recipes ranged from Sheep's Head Broth to A Pudding made of Small Birds - the type of dishes people are too squeamish to make today," says Gray.

He recommended starting the day with pumpkin porridge, which involved little more effort than simmering chunks of pumpkin with a little butter and water and adding a little milk before eating.

"Cheap eating largely revolved around loading up on carbohydrates to fill you up so you didn't need too much meat, which was much more expensive," says Gray.

An old Scottish recipe for Fitless Cock was equally economical as it contained no meat. It was a chicken-shaped oatmeal pudding which "fooled no-one", says food writer Stefan Gates.

To make Fitless Cock mix together oatmeal, shredded suet and a finely chopped onion with a beaten egg. Form into the shape of a chicken, wrap in cloth and boil for two hours.

A similar recipe dates from World War II, when the Ministry of Food introduced rationing to cope with food shortages. As the system gathered momentum, the ordinary ration came to encompass meat, cheese, butter, margarine, bacon and ham, tea, preserves, sugar and cooking fats such as lard.

To help war-weary home cooks, its austerity recipes ran in newspapers and on its daily radio broadcast. As well as mock cream and myriad uses for spam and dried egg, it devised this recipe for mock goose, complete with stuffing.

150g (6oz) cup dried lentils

1/2 pint water

a little lemon juice

salt and pepper to taste

for the stuffing - breadcrumbs (made from two slices), chopped onion, fresh sage

Simmer the lentils until all the water has been absorbed. Add lemon juice and season. Then to make the stuffing fry the onion in a little water, drain and add breadcrumbs and chopped sage. Place half the lentil mixture in an ovenproof dish, then layer on the stuffing and top with the remaining lentils. Cook at 180C (356F) until crisp.

Accompany with boiled potatoes and shredded cabbage cooked in a modicum of water. Reserve the cooking liquor to make gravy. Doesn't appeal? Tough.

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Oysters used to be food for the poor

When the Titanic set sail in April 1912, its hold was loaded with goodies such as wine and fresh asparagus. But not all passengers dined on such fine fare. A typical dinner menu in steerage included rice soup with cabin biscuits and corned beef.

Rice soup was made with chicken stock, rice, onion and celery, with salt and pepper to taste. After two hours in the pot, it was strained and cream or milk added.

And finally, how about something sweet for afters - a carrot, perhaps? Mrs Beeton recommended a recipe for carrot jam for those unable to afford fruit. In WWII carrots stood in for stone fruits in desserts such as apricot flan, or were made into carrot fudge with gelatine to set and orange squash for flavouring.

But some recipes do not translate today because cheapness changes over time, says Emily Angle, editor of the BBC Food website.

"Oysters were food for the poor until they were all eaten. Their rareness transformed them into food for the rich."